The present invention relates to systems and methods for connecting a crane suspension assembly to a support column on a crane. More particularly the present invention relates to systems and method for connecting a pendant to an intermediate location on a crane boom.
Lift cranes typically include a carbody; ground engaging members elevating the carbody off the ground; a rotating bed rotatably connected to the carbody such that the rotating bed can swing with respect to the ground engaging members; and a boom pivotally mounted on the rotating bed, with a load hoist line extending there from. For mobile lift cranes, there are different types of moveable ground engaging members, most notably tires for truck mounted cranes, and crawlers. Typically mobile lift cranes include a counterweight to help balance the crane when the crane lifts a load. Typical cranes include a boom suspension that is used to change the angle of the boom and provide tension forces to offset the forces applied to the boom by the load on the load hoist line so that the boom can behave as a column member with only compressive forces acting through the length of the boom.
Typical cranes are designed to be set up with different boom length configurations to optimize the capacity that the crane can handle, only using as long of a boom as is necessary for a particular lift operation that the crane is being set up for. Since the boom length will vary between different configurations, the boom suspension also has to be designed to accommodate different boom lengths. Typically the boom suspension includes multiple sections of suspension members that are connected together, sometimes referred to as boom backstay straps, which connect between the top of the boom and either an equalizer suspended between the boom and a fixed mast, or between the boom and the top of a live mast. The suspension member may be rigid such as steel bars or may be flexible such as wire or synthetic rope. On a crane with a relatively long boom, the suspension may additionally be connected to the boom at an intermediate location less than the top of the boom. On a typical crane with a fixed mast, the boom hoist rigging has multiple parts of line that run between the equalizer and the top of the mast, and is used to control the angle of the boom.
Since the crane will be used in various locations, it needs to be designed so that it can be transported from one job site to the next. This usually requires that the crane be dismantled into components that are of a size and weight that they can be transported by truck within highway transportation limits. The ease with which the crane can be dismantled and set up has an impact on the total cost of using the crane. Thus, to the extent that fewer man-hours are needed to set up the crane, there is a direct advantage to the crane owner or renter.
It is convenient to transport the sections of the boom straps and jib backstay straps with the sections of boom between one job site and the next. This is because, for the most part, the number of sections and the length of each section of the boom straps and the jib backstay straps that will be needed are dependent on the number and lengths of the boom sections that are used to construct the boom. For example, a 100 foot boom may be made from a 10 foot boom butt, a 10 foot boom top and four 20 foot boom inserts. However, if the boom is going to be 120 feet long, five 20 foot boom inserts will be used. If the boom is going to be 130 feet long, five 20 foot inserts and one 10 foot insert will be used.
A typical boom insert has connectors at each end for connection to an adjacent crane section. The connectors are typically tabs having an aperture for receiving a pin. A boom insert may have complementary connectors at each end of the boom insert. For example, a near end of the boom insert may have single tabs with an aperture. A far end of the boom insert may use sets of tabs spaced apart by the thickness of the tab on the first end. Thus when the boom inserts are placed together end to end, the single tab of the first end may be orientated between the two tabs of the second end with their apertures aligned. A pin is then inserted through the apertures coupling the boom inserts together. To aid in alignment of the boom inserts during assembly, the tabs on an upper side of a boom insert may be replaced by bracket and pin. The far end of the boom insert may have a bracket on the upper side with the bracket opening upward. The near end of the boom insert may have a horizontal pin complementary to the bracket. Two boom connections may then be assembled by joining the bracket and pin with the boom inserts angled relative to one another. Then, with the pin in the bracket, the boom insert is rotated until the tabs on the lower section are aligned. A pin is then inserted into the aperture of the tabs and the boom sections are coupled together.
When an intermediate suspension connection to the suspension is required, an intermediate suspension connector such as a pendant assembly is used to join the suspension to the boom. The pendant assembly connects to the boom at the connection between adjacent boom inserts. Typically, the lower pins are replaced by longer pins. The pendant assembly has tabs on its lower end that are spaced apart the width of the outer tabs of the boom insert. Thus when the boom is assembled, the boom inserts are coupled together as described previous with the exception that the pendant assembly is placed over the tabs of the boom insert. Apertures in the pendant tabs are aligned with the apertures in the boom insert tabs and the longer pin is inserted through the pendant tabs and the boom insert's tabs. The longer pin couples the boom inserts together along with the pendant assembly.
The described system of attaching a pendant assembly to a boom is advantageous in that it requires no special parts other than the pendant assembly and the longer pins. If the pendants assembly is not required, it is simply not attached between boom sections. However, assembly of the crane sections is complicated by the additional alignment necessary with the pendant assembly. Also, because the pendant assembly is a separate component, there exists the possibility that the pendant assembly may be lost or unavailable when assembling the boom. The assembly of the boom cannot be completed until the pendant is in place. Therefore there would be a great benefit if it were possible to attach the boom to the suspension using a method that did not require a pendent coupled to the ends of a boom. Further, by simplifying the connection of the boom inserts when a pendant is required, the amount of time it takes to assemble a boom may be shortened and potential delays reduced.